Emulsions in Industry
Lipid phases, such as oils or fats are common ingredients used in many different products. In order to give the lipid phase containing products an acceptable physical homogeneity and ‘shelf-life’ (oil and water do not mix with each other) the bulk lipid phase has to be broken up into small droplets, i.e. the lipid phase has to be dispersed into an aqueous continuous phase. The obtained product is an oil-in-water emulsion. The dispersed oil droplets are stabilised by surface active molecules which form a stabilization layer around the oil droplets. Both oil-in-water and water-in-oil emulsions can be formulated depending on the solubility of the used surface active molecules (also denoted as emulsifiers) which stabilize the dispersed phase droplets. Oil-in-water emulsions are stabilized by hydrophilic surface active molecules, whereas water-in-oil emulsions are stabilized by lipophilic emulsifiers.
In order to make stable and/or homogeneous oil-in-water emulsions, the oil phase has to be dispersed as small oil droplets having a radius from ca 100 nm up to several hundreds of micrometers, into the continuous aqueous phase. For this, homogenisers, i.e. machines which are able to add high energy to the oil-water mixture are necessary to use. The formation of the stabilization layer around the oil droplets during the homogenisation step renders the oil droplets kinetically stable against coalescence, flocculation, coagulation, Ostwald ripening or creaming. The surface active material used in oil-in-water based emulsion products can either be low molecular weight hydrophilic surfactants, such as polysorbates, lysolecithins, etc., or polymers, such as proteins, e.g. gelatin or from milk, soya, or polysaccharides, such as gum arabic or xanthan, or (nano or micro)-particles, such as silica particles, or mixtures thereof.
Oil-in-water emulsion based products are ubiquitous in—Food, Cosmetics, Pharmaceuticals or Agro-chemicals. Prominent oil-in-water emulsion-based food products are for instance milk, mayonnaise, salad dressings, sauces or clinical products. Prominent oil-in-water emulsion-based products used in the cosmetical or pharmaceutical Industry are lotions, creams, milks, pills, tablets, dragees etc. The oil droplets in such products are usually made of lipids, for instance, triglycerides, diglycerides, waxes, fatty acid esters, fatty acids, alcohols, mineral oils, or hydrocarbons.
Use of Emulsions
Emulsions are used either as a starting material, intermediate or final product or as an additive to a final product.
One of the uses of emulsions in Industry is to deliver active compounds or functional molecules, such as, flavours, vitamins, antioxidants, neutraceuticals, phytochemicals, drugs, chemicals, etc. Administration of the active components requires the use of an appropriate vehicle for bringing an effective amount of the active component into the product and/or desired place of action. Oil-in-water emulsions are commonly used delivery systems since they take advantage of the increased solubility of lipophilic active compounds in the oil with respect to water. In EP 1116515, as an example of using emulsions for controlling flavour performance, a hydrophobic active ingredient, such as a flavour component, is mixed into a matrix via an extruder in form of an oil-in-water emulsion in order to increase the stability of the introduced active ingredient during further processing of the product. In WO 00/59475, as an example for a pharmaceutical oil-in-water emulsion, a composition and method for improved delivery of ionizable hydrophobic therapeutic agents is described, which are mixed together with an ionizing agent, a surfactant and a triglyceride to form an oil-in-water emulsion. WO 99/63841, as an example for the use of emulsions in the food area, describes compositions comprising phytosterol having enhanced solubility and dispersibility in an aqueous phase due to the formation of an emulsion or a microemulsion.
Another reason to disperse a lipid into an aqueous phase in form of an emulsion is to create a homogeneous and kinetically stabilized oil and water containing product. This is a need in the manufacture of a great variety of different products: For instance, in ice cream production during the preparation of the ice cream mix before freezing, in the production of mayonnaise, sauces, dressings, creams, lotions, sprays and in lots of more oil containing products in which a lipid phase has to be incorporated into an aqueous continuous phase to obtain a kinetically stable and homogeneous intermediate or end product. One drawback in all these applications is that the oil-water mixture has to be treated with high energy in order to get a sufficient dispersibility of the oil phase, i.e., it is necessary to use specific and sometimes expensive and sophisticated ‘high energy input’ machines e.g. homogenisers, high shearing mixers, ultrasound, jet mixers etc. to obtain the stable emulsion.
The situation gets critical if no homogeniser or other high energy input machine is available or can be used for the kinetical stabilization of the water-oil mixture. One class of products which suffers from this fact are the Instant or Kitchen products, which usually can be prepared with only manual operation, e.g. shaking or stirring. Instant products are well-known to the consumer. They are well-accepted products since their preparation is easy and does not require the use of sophisticated high energy mixers. Examples are instant soups, spices, pastes, seasonings, butter substitutes, etc. They are based on the principle of adding a concentrated stock composition (paste, powder, liquid) to a product of choice during food preparation at home or in a restaurant. The so prepared products have the disadvantage that they have only a limited storage stability, since the lipid phase is distributed in the product in a inhomogeneous way leading quickly to extensive phase separation after preparation. This sort of instability or inhomogeneity in the prepared product is mainly observed when the Instant products contain oil or other lipidic components. Therefore, the word ‘inhomogeneity’ describes the fact that the oil phase is not distributed in a homogeneous, i.e., uniform, way throughout the product. This situation can be easily visualized by light microscopy, which allows to localize the oil/fat due to specific oil coloration technology. If the oil inhomogeneity is quite significant, non-dispersed macroscopic oil patches can be observed also by eye.
In general, oil-based ingredients show insufficient dispersion properties when added to water or water based products without applying a high energy process. Manual operation generally is not sufficient to get a stable product, therefore, leading to the formation of very heterogeneous emulsions that quickly phase separate and physically destabilize. The inhomogeneity of the oil containing product is due to the fact that the created emulsion droplets are very large (hundreds of microns) and polydisperse when using low energy mixing.
U.S. Pat. No. 4,160,850 describes a mix suitable for the consumer preparation of a spreadable butter-substitute product. The final product in this case is a water-in-oil emulsion. The mix consists of a mixture of a hard fat, an oil and a water-in-oil emulsifier, which is added to the oil/fat phase to stabilize the water phase which is added by the consumer during in home preparation of the butter-substitute using a conventional home mixer to form a water-in-oil emulsion. These products are quite unstable when stored at room temperature and have to be refrigerated to improve the product stability.
WO 03/053149 A1 discloses a method for the preparation of a spreadable oil and water emulsion comprising mixing a base composition with oil and/or water by a simple manual operation. The base composition comprises a cold hydrating viscosifying agent, such as the cold hydrating starch or a polysaccharide, a hydrophilic emulsifier, such as hydrolysed lecithin, or caseinate or a caseinate replacer, and optionally an acidifying agent. The presence of the viscosifying agent, especially the polysaccharide in the base composition leads to products with smaller average oil droplet size in a final oil-in-water emulsion.
If the oil droplets in the oil-in-water emulsions are ultra small, e.g. in the order of several nanometers to about 200 nm diameter, and spontaneously formed (without the use of a high energy intake device) the emulsion is called an ‘oil-in-water microemulsion’ (Evans, D. F.; Wennerström, H. (Eds.); ‘The Colloidal Domain’, Wiley-VCH, New York, (1999)). These emulsions are clear and thermodynamically stable and, therefore, are for the man skilled in the art different from ordinary emulsions the latter being thermodynamically unstable and generally turbid.
JP 2004 008837 discloses an oil in water emulsion which contains water-soluble solid particles present in the oil droplets. The particles are in the size range of 20 nm to 10 μm. The particles are prepared in a water-in-oil (w/o) emulsion by means of dehydration (i.e., not a spontaneous process) before the whole particle/oil (S/O) suspension is dispersed in an aqueous phase using the porous membrane emulsification process.
WO 02/076441 discloses the use of an alcohol-in-fluorcarbon microemulsion as a precursor for the preparation of solid nanoparticles. The nanoparticles have a diameter below 200-300 nanometers. Nanoparticle formation is not spontaneous and triggered by cooling the precursor microemulsion below about 35° C., or by evaporating the alcohol in the precursor microemulsion or by diluting the microemulsion with a suitable polar solvent.
US 2004/022861 discloses a w/o/w double emulsion, in which the oil droplets containing an aqueous microscopic water phase containing protein or another hydrophilic agent. The whole double emulsion is sprayed into, for instance, liquid nitrogen via a capillary nozzle for production of protein-loaded microparticles.
All these examples describe the non-spontaneous formation of solid hydrophilic (nano)particles using w/o microemulsions or w/o or w/o/w double emulsions and needing an external trigger for the solidification of the hydrophilic domains inside the oil droplets. After preparation of the (nano)particles they are largely unaffected by environmental factors such as temperature, pH, or external fluid properties. It has to be mentioned that ordinary w/o microemulsions in which the water droplets are not solidified, i.e. fluid, are largely affected by such environmental factors.
It is the objective of the invention to provide a new solution which allows to disperse a lipidic phase into an aqueous phase to form an oil-in-water emulsion without using a high energy intake mixing machine, but only a manual operation, such as hand shaking or hand stirring with a spoon or an equivalent low energy device which is used in the kitchen, restaurants or in Food Service devices. A low energy device can be also selected from methods allowing to form oil droplets using membrane emulsification, nano- and microfluidics devices or static mixers. The lipidic phase used for making the emulsion of this invention is easy to prepare and does not need sophisticated mixing equipment.